1. Field of the Invention
This invention relates to a control system for an automatic vehicle transmission, particularly to a control system for controlling the current supply to an actuator such as a solenoid valve when the engine and the vehicle are stopped.
2. Description of the Related Art
Automatic vehicle transmissions are commonly shifted by using linear solenoid valves (actuators) to operate hydraulic clutches. A technology for this is taught, for example, by Japanese Patent Publication No. Hei 5(1993)-17,430. Upon being supplied with current, the linear solenoid valve supplies the hydraulic clutch with hydraulic pressure proportional to the magnitude of the supplied current so as to engage the hydraulic clutch and shift gears.
In an ordinary vehicular engine, the ignition switch has an OFF position, an ACC position on which on-board audio devices, etc., operate, an ON position on which other devices such as a window motor, air conditioners operate and a START position on which the engine starter motor operates to start the engine. When the ignition switch is turns from the OFF position to the ON position, the current supply to the linear solenoid valve is started before the engine crankshaft begins to rotate.
Since the engine has not started, no oil (automatic transmission fluid or ATF) is supplied to the linear solenoid valve at this instance. Nevertheless, the valve plunger begins to move freely in response to the current supply to produce a noise due to the operation, thereby disadvantageously degrading the silence or quiet in the passenger room. When the engine starts, it supplies oil to the solenoid valve and the noise is canceled by a dampening effect of the oil.
Thus, for example, when the driver turns the ignition switch from the OFF position to the ON position to open an electrically-controlled window, the current supply to the solenoid produces a noise which may be annoying to the driver. In such a case it would be preferable to delay the energization of the solenoids while, on the other hand, the automatic transmission should preferably initiate its operation quickly when the ignition switch is further turned to the START position.